Several methods and types of knitting machines are known which can be used to knit courses alternatingly from one of at least two pile threads together with one base thread.
According to German Patent No. 671,333, two pile threads are successively fed to one of two alternate sets of needles, while the base thread is fed to all needles. As a result, the pile thread, which is fed first of all, will be arranged in a wave-like manner in front of and behind the needles. This will strain the pile thread in an uncontrollable manner during the knitting action. As a consequence of this tensioning, special requirements of the pile-yarns, such as requiring a high tenacity yarn, are necessary. Also, the different tension of the pile threads will effect the pile forming ability of each pile thread to form different pile lengths.
The wave-like arrangement of the first pile thread is approximately realized by an extraordinary adjustment of the feeding tubes, using needles with plating angle hooks and a constant feeding speed of the pile thread which results from the preferred stitch construction. If an individual needle selection is preformed, the feeding speed of the pile thread is extraordinarily different according to pile knitting or missing so that vibrations of the pile thread will occur and will prevent a regular feeding to the predetermined needles only. Also, each negligible deviation from the position of the needles or the feeding tubes will damage these parts and leads to additional faults in the fabric.
By a method according to FIG. 18 to 21 of U.S. Pat. No. 4,633,683 (based on German Patent No. 30 24 705) the feeding of the pile threads is improved by the presence of a larger space between the alternate needle sets. Nonetheless, undesirable straining or tensioning of the first fed pile thread still exists because of the wave-like arrangement established in the yarn due to its being positioned before and behind the needles until the thread is knitted. Similarly, the depending disadvantages of such tensioning of the pile yarn, as described before, still exist.
In U.S. Pat. No. 4,307,586 (based on the German Patent Specification No. 23 43 886) it is proposed to feed pile threads in a way that is analogous to the distribution of pile fibers on sliver knit machines. In succeeding feeders only a pile thread is fed to selected needles raised to their clearing position and which are then retracted to an intermediate (feeding) position until at the last feeder of a knitting cycle base thread is fed to all needles which are subsequently retracted to the knock over position.
The method described in this '586 patent is, however, characterized by the same disadvantages as German Patent No. 671,333 and U.S. Pat. No. 4,633,683. In these a correct arrangement of the pile threads before selected and behind undelected needles is impossible. Also, after feeding a pile thread to the raised selected needles and the retraction of these needles with their hooks to the intermediate position of all needles, the pile thread will rest on the hooks of the unselected needles and can slip uncontrollably before or behind these hooks. This result is sometimes assisted by the vibrations of the pile thread depending on its shortly changing feeding speed. Sinkers to control the arrangement of the pile threads are not provided. The wave-like arrangement of the pile threads from the feeding to the knitting action will also strain these threads uncontrollably so that breakage may occur. Contrary to the described feeding of a base thread during the production of sliver knit fabrics, the base thread for a pile or plush fabric must be fed underneath the sinker nebs.
Nowhere does the U.S. '586 patent set forth a way in which the base thread is fed underneath of the sinker nebs and it is simultaneously avoided that the previously fed pile threads will remain in place over of the nebs of the retracted sinkers, so that pile loops are drawn from the pile threads simultaneously to the knitting action of the needles.
To avoid the above referred disadvantages of these foregoing methods German Patent Specification No. 23 22 384 suggests that each pile thread be knit to stitches subsequent to the feeding. This method is practiced on a machine having a cylinder and dial, and the base thread is fed at first to all dial and cylinder needles. While the dial needles are knitting preferably longer stitches, the cylinder needles are retracted to an intermediate position, in which the base yarn is looped, but the clearing of the previously knitted stitches is prevented ("tuck on the latch"-position). In at least two subsequent steps in each case selected needles are raised to engage a pile thread and are retracted to their knock over position, knitting stitches from the base and pile thread and simultaneously drawing pile loops. Additional base thread for the stitches of the cylinder needles is robbed from the enlarged dial stitches. The advantages of this method are that the base thread is prelooped in the first feeder for subsequent knitting actions together with one of the pile threads and that the pile threads are knit to stitches in the same feeder in which they are fed.
The disadvantages of this approach is that the resulting fabric is characterized by a rib-construction, which reduces the pile density, and that the pile loops must protrude between the wales of the cylinder needles.
The method according to U.S. Pat. No. 4,612,784 (based on German Patent No. 31 45 307) will transfer the fundamental steps of the German Patent Specification No. 23 22 384, under consideration of U.S. Pat. No. 3,406,538, in which also all threads knitted to a course are pre-looped and which is an improvement of U.S. Pat. No. 2,094,180 in which part of threads knitted to a course are pre-looped, to a multifeed circular knitting machine with cylinder and sinker ring.
Analogous to the foregoing referred specifications the base thread and at least two pile threads are fed and prelooped in succeeding feeders by retracting the needles to the "tuck on the latch" position. All needles are raised for clearing and after feeding the base thread the needles are retracted, prelooping the base thread over the ledges of the loop sinking plates. In subsequent feeders selected needles are raised for engaging a pile thread, without clearing the loops of the base thread from the latches, and are then retracted again to the "tuck on the latch" position, prelooping the pile threads over the ledges of the knock-over plates which are also operating as holding down sinkers for the loops of the base thread. Subsequent to the feeding and pre-looping of the pile threads both sinkers ("plates") are actuated outwardly to clear the loops of the base and the pile threads from the ledges, and the knock over action of the needle is completed.
The advantages of this method are the reliable feeding of all threads with controllable tension and the pre-looping of all threads immediately following the feeding. The disadvantages are the great extent of a knitting cycle based on the prelooping actions of all threads which reduces the production capacity and the necessarily coordinated adjustment of the prelooping cams to the stitch cam.
The pre-looping of the ground thread is indispensible in this concept since it is only through the higher position of the loops of the base thread that, without clearing the base thread from the latches, the needles may be raised sufficiently to have the pile thread fed into their hooks. Therefore, extended raising and retracting movements of the needles are stipulated and a reduced number of feeders will result.
A further fundamental disadvantage of this method is that the pre-looped loops of the base and pile threads must be cleared from the corresponding sinker ledges during knitting by retracting the sinkers with their nebs in front of the needles, and, for that reason, the formation of the pile loops cannot be controlled in this decisive and critical moment. Immediately after the knock-over action of the needles, the pile loops are engaged by the sinker nebs of the sinking plates and post-tensioned to obtain a satisfactory uniformity of the pile loops while the needles remain in idle position. This process, however, necessitates a certain minimum length of the pile loops and, therefore, excludes the production of short pile loops.
During knock-over it is also possible that pile loops which are directly connected with the feeder by floats can be deformed or distorted by irregular tensioning of the pile threads.